Quantum Entanglement & Nonlocality

In quantum theory, certain physical systems can become "entangled," meaning that their states are directly related to the state of another object somewhere else. When one object is measured, and the Schroedinger wavefunction collapses into a single state, the other object collapses into its corresponding state ... no matter how far away the objects are (i.e. nonlocality).

Einstein, who called this quantum entanglement "spooky action at a distance," illuminated this concept with his EPR Paradox.